Wheelock — Nature of Ionization Produced hy a Rays. 255 



(3) The equation obtained by assuming colunitiar ionization 

 with the ions imiformly distributed within the cohimns, does 

 not represent the curve experimentally obtained with the par- 

 allel field. The experimental curve lies below the calculated 

 curve, except for small potential gradients, when the ordinary 

 Bragg cliamber is used. 



(4) The lack of agreement between the experimental and 

 calculated results is not due to an inclination of some of the 

 columns in the ionization chamber. 



(5) The lack of saturation obtained at different parts of the 

 range, when the field is ajjplied parallel to the path of the 

 ionizing a particle, is not completely accounted for by initial 

 recombination ; neither does columnar ionization completely 

 explain the results obtained with the perpendicular field. 



(6) The saturation value of the current is obtained more 

 easily as the pressure of the gas is diminished. This would be 

 expected on either hypothesis. However, the results obtained 

 appear to indicate that the lack of saturation is not all due 

 to the effect of general recombination of the ions within the 

 columns. 



(7) Undoubtedly a considerable part of the anomalous behav- 

 iour of the ions produced by a rays (in respect to saturation, 

 etc.) is due to the columnar arrangement of the ions ; it is pos- 

 sible that this would be sufficient to account for all the facts if 

 the distribution of the ions within the columns were known. 

 On the other hand, it appears probable that certain outstanding 

 discrepancies may be due to initial recombination. 



In conclusion, I wish to express my gratitude to Professor 

 H. A. Bumstead, at whose suggestion these experiments were 

 undertaken, for his many valuable suggestions and kindly 

 interest in the work. 



